Dual Grow Light Mount

I had different type of these EWITTI LED Grow Lights (ASIN= B0DM5LHXB5), the one with the samll mount and the other other one with the telescope pole.So, I came up to design my own base where the telescope pole fits in (and the flower pots can be used as additional weight) and I also wanted to have both grow light on top of that pole. Now, the lights have a regular ¼" UNC thread (same as most cameras, rigs etc have) so you can use the same screws here, ideally with a 3/8 length, you can find them easily on AMZN, search for UNC 1/4"-20 x 3/8" (i.e. here or a package with different sizes)The telescope pole has seems to have 0.390"-27 UNS thread andI couldn't find a nut or a brass thread insert (in Europe) so I modele